nlist.ml

type 'a succ = private S
type z = private Z

type ('elt,'size) t = 
| []: ('elt, z) t
| (::): 'elt * ('elt,'size) t -> ('elt, 'size succ) t

let rec map2: type size. ('elt -> 'elt2 -> 'elt3) -> ('elt,size) t -> ('elt2,size) t -> ('elt3,size) t = fun f x y ->
match x,y with
| a :: q, b :: q' -> (f a b) :: map2 f q q'
| [], [] -> []
| _ -> .